Negative 30 degrees (which is nearly the same temperature in celsius or fahrenheit) is pretty darn cold. Even a healthy, fully-charged battery will struggle to turn an engine over in those temps. The cold-cranking-amps test for batteries is performed at zero degrees fahrenheit (-18 degrees C). So, minus 30 degrees is well below this, regardless of which scale you use.
If your car has sat for several days in these temperatures, I would be surprised if you could start it without spending an hour or two on a block heater.
If the car has a block heater installed (I assume it does, since you mentioned plugging it in), I would first recommend finding a way to plug it in and let the block heater work for a couple of hours. Then try starting it again. If it still won't start, then I would find a way to try and jump start it (make sure the block heater has run for an hour prior to jumping it, too).
Something else you can try (if you're comfortable doing so) is to remove the battery from the car and bring it inside to warm up for a few hours. Maybe even put it on a trickle charger while it warms up, too, to make sure it has a good charge. Then put it back in the car and try to start it.
If you manage to get it started, I would recommend driving to the nearest auto parts store and ask them to test the battery. It's probably toast, and you'll want a new one.
As a long term solution, it might be a good idea to get a battery blanket (a sort of electric blanket for your battery) to go along with the block heater. In extremely cold temperatures, you can plug it in and warm up your battery, which will help with cold starts in extreme temperatures.